The geology of the Mt Stroker area, Eastern Otago

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Abstract
Tertiary rocks occurring as several small outliers resting on schist, south-east of Middlemarch, are mapped and separated into two formations. The Summer Hills Formation, probably Miocene in age, is composed of indurated and friable quartz sandstones and conglomerates. It contains material from the underlying Otago schist, but also orthoclase and p.erthitic microcline from a plutonic terrain. It rests on a slightly dissected schist erosion surface and is overlain, apparently conformably, by basanitic volcanic rocks of the Waipiata Formation, of late Miocene or early Pliocene age. The basanites are chemically and mineralogically similar to the majority of volcanic rocks peripheral to the central Dunedin complex. They contain gabbroic, pyroxenitic, and peridotitic fragments, and also partly assimilated quartz xenoliths. Low-angle, north-west-striking thrust faults and high-angle, north-east-striking faults occur in the area. The latter are apparently related to Otago basin-and-range structures. An early erosion surface is correlated with Cotton's Cretaceous peneplain; a later erosion surface was formed after the volcanic activity but before initiation of the present youthful drainage,

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